Old amplifier problem

Discussion in 'General Electronics Chat' started by frusciante89, Jun 26, 2013.

  1. frusciante89

    Thread Starter New Member

    Nov 13, 2012
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    Hi everybody, I have a problem with my my 1030...
    I bought it used in the US and I immediately changed all the capacitors...
    I then got back to my country (Italy) and I decided to change the transistors as well, since the amplifier was making a very strange noise...
    I then bought a transformer (200 Watts) In order to adapt the power cord to the Italian plug. I was finally able to switch it on and everything works fine, it sounds very crisp and clear... however there is an annoying charge on the front plate: it's not electrocuting, but you can definitely feel it... I noticed that when the iPod is connected to the auxiliary wire, and I touch at the same time the metal case of the iPod and the front plate, then this effect disappears...
    Does anybody have an explanation for this? Could it be because the power cord is only a two way? I was thinking of replacing the power cord with a 3 way and hook the ground prong to the chassis: would it make any difference?
    Another thing I can think of is that I made some kind of mistake in the transistors substitution...
    What do you suggest?
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,980
    744
    If the Chassis is Live then its because there is no Earth or it has a live chassis design. Better to replace the mains lead for a 3 wire type and Earth it.
     
  3. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
    197
    If it's a Marantz 1030 then it has a 2.2meg resistor from 1 leg of the AC supply to ground. That explains the tingle.
     
  4. atferrari

    AAC Fanatic!

    Jan 6, 2004
    2,648
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    Hi TG. What is the use of that?
     
  5. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
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    Old equipment with 2 wire AC power cords frequently had a high-value resistor or a high impedance AC-rated capacitor (like .047uf) connected this way to provide a low current high-z ground reference.
    Reversing the AC cord in the wall can eliminate the tingle.

    I don't know about other countries but in the early days the US only had 2-wire, (and I recall) non-polarized mains outlets.
     
    Last edited: Jun 26, 2013
  6. frusciante89

    Thread Starter New Member

    Nov 13, 2012
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    So what should I do? Use a 3 prong wire? Can you explain what the 2.2 MOhms is doing exactly?
     
  7. BobTPH

    Active Member

    Jun 5, 2013
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    Supposedly keeping the at the potential of the neutral wire, but in your case it is do keeping at the potential of the live wire. Take it out, use a 3 prong plug and connect the case to the ground lead.

    Bob
     
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